Polishing composition and method of polishing a substrate having enhanced defect inhibition

ABSTRACT

An aqueous alkaline chemical mechanical polishing composition includes a quaternary phosphonium compound having aromatic groups which enables enhanced reduction of defects on silicon oxide substrates and enables good silicon oxide removal rates during chemical mechanical polishing. The chemical mechanical polishing composition is stable.

FIELD OF THE INVENTION

The present invention is directed to an alkaline polishing compositionand method of polishing a substrate having enhanced defect reductionwith good dielectric removal rates. More specifically, the presentinvention is directed to an alkaline polishing composition and method ofpolishing a substrate having enhanced defect reduction with gooddielectric removal rates, wherein the polishing composition includesquaternary phosphonium compounds having aromatic groups to enhance thereduction of defects on substrates which include dielectrics of siliconoxide, and wherein at least some of the silicon oxide is removed fromthe substrate.

BACKGROUND OF THE INVENTION

In the fabrication of integrated circuits and other electronic devices,multiple layers of conducting, semiconducting and dielectric materialsare deposited on or removed from a surface of a semiconductor wafer.Thin layers of conducting, semiconducting, and dielectric materials canbe deposited by several deposition techniques. Common depositiontechniques in modern processing include physical vapor deposition (PVD),also known as sputtering, chemical vapor deposition (CVD),plasma-enhanced chemical vapor deposition (PECVD), and electrochemicalplating (ECP).

As layers of materials are sequentially deposited and removed, theuppermost surface of the wafer becomes non-planar. Because subsequentsemiconductor processing (e.g., metallization) requires the wafer tohave a flat surface, the wafer needs to be planarized. Planarization isuseful in removing undesired surface topography and surface defects,such as rough surfaces, agglomerated materials, crystal lattice damage,scratches, and contaminated layers or materials.

Chemical mechanical planarization, or chemical mechanical polishing(CMP), is a common technique used to planarize substrates, such assemiconductor wafers. In conventional CMP, a wafer is mounted on acarrier assembly and positioned in contact with a polishing pad in a CMPapparatus. The carrier assembly provides a controllable pressure to thewafer, pressing it against the polishing pad. The pad is moved (e.g.,rotated) relative to the wafer by an external driving force.Simultaneously therewith, a polishing composition (“slurry”) or otherpolishing solution is provided between the wafer and the polishing pad.Thus, the wafer surface is polished and made planar by the chemical andmechanical action of the pad surface and slurry.

Certain advanced device designs demand polishing compositions thatprovide enhanced silicon oxide removal efficiency at lower point-of-use(POU) abrasive weight % as well as reduced scratch defects for theimprovement of polishing processes throughout and product yield %. Asthe size of structures on semiconductors devices continue to shrink,performance criteria which was once acceptable for planarizing andreducing defects of polishing dielectric materials becomes increasinglyless acceptable. Scratches which were once considered acceptable aretoday becoming yield limiting.

Accordingly, there is a need for polishing compositions and polishingmethods that exhibit desirable planarization efficiency, uniformity, anddielectric removal rate while minimizing defects such as scratches.

SUMMARY OF THE INVENTION

The present invention provides a chemical mechanical polishingcomposition consisting of water; an abrasive; optionally a pH adjustingagent; optionally a biocide; a pH greater than 7; and a quaternaryphosphonium compound having formula (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, Cl⁻, I⁻, F⁻ and OH⁻.

The present invention also provides a chemical mechanical polishingcomposition consisting of water; 0.1 to 40 wt % of an abrasive;optionally a pH adjusting agent; optionally a biocide; a pH greater than7; 0.001 to 1 wt % of a quaternary phosphonium compound having formula(I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, Cl⁻, I⁻, F⁻ and OH⁻.

The present invention further provides a chemical mechanical polishingcomposition consisting of water; 5 to 25 wt % of a colloidal silicaabrasive; a pH adjusting agent; optionally a biocide; a pH of 8-13; 0.01to 1 wt % of a quaternary phosphonium compound having formula (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, Cl⁻, I⁻, F⁻ and OH⁻.

The present invention provides a method for chemical mechanicalpolishing of a substrate, comprising: providing a substrate, wherein thesubstrate comprises silicon oxide; providing a chemical mechanicalpolishing composition consisting of water; an abrasive; optionally a pHadjusting agent; optionally a biocide; a pH greater than 7; a quaternaryphosphonium compound having (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, Cl⁻, I⁻, F⁻ and OH⁻; providing a chemicalmechanical polishing pad with a polishing surface; creating dynamiccontact at an interface between the polishing surface of the chemicalmechanical polishing pad and the substrate with a down force of 3 to 35kPa; and dispensing the chemical mechanical polishing composition ontothe chemical mechanical polishing pad at or near the interface betweenthe chemical mechanical polishing pad and the substrate; and whereinsome of the silicon oxide is removed from the substrate.

The chemical mechanical polishing composition and method of the presentinvention enable enhanced reduction of defects, enable good siliconoxide removal rate and the chemical mechanical polishing composition isstable.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification the following abbreviations havethe following meanings, unless the context indicates otherwise:L=liters; mL=milliliters; kPa=kilopascal; Å=angstroms; nm=nanometers;min=minute; rpm=revolutions per minute; wt %=percent by weight;RR=removal rate; mmol=millimoles; Br⁻=bromide; Cl⁻=chloride; I⁻=iodide;F⁻=fluoride; OH⁻=hydroxide; PS=Polishing Slurry of the Invention;PC=Comparative Polishing Slurry.

The term “chemical mechanical polishing” or “CMP” refers to a processwhere a substrate is polished by means of chemical and mechanical forcesalone and is distinguished from electrochemical-mechanical polishing(ECMP) where an electric bias is applied to the substrate. The term“TEOS” means the silicon oxide formed from the decomposition oftetraethyl orthosilicate (Si(OC₂H₅)₄). The term “composition” and“slurry” are used interchangeably through-out the specification. Theterm “halide” means chloride, bromide, fluoride and iodide. The terms“a” and “an” refer to both the singular and the plural. All percentagesare by weight, unless otherwise noted. All numerical ranges areinclusive and combinable in any order, except where it is logical thatsuch numerical ranges are constrained to add up to 100%.

The chemical mechanical polishing composition of the present inventionis useful for polishing a substrate comprising silicon oxide. Thechemical mechanical polishing composition consists of water; anabrasive; optionally a pH adjusting agent; optionally a biocide; a pHgreater than 7; and a quaternary phosphonium compound for reducingdefects and enhancing the removal rate of silicon oxide from a substratehaving formula (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, Cl⁻, I⁻, F⁻ and OH⁻. The term “enhanced siliconoxide removal rate” used herein describes the removal rate of siliconoxide (for removal rate measured in A/min) resulting from polishing asubstrate with the chemical mechanical polishing composition containinga quaternary phosphonium compound with an aromatic group means that atleast the following expression is satisfied:A>A₀wherein A is the silicon oxide removal rate in Å/min for a chemicalmechanical polishing composition containing a claimed quaternaryphosphonium compound used in the method of the present invention ofpolishing a substrate, as measured under the polishing conditions setforth in the Examples; A₀ is the silicon oxide removal rate in Å/minobtained under identical conditions with only silica abrasives present.

The term “improved polishing defectivity performance” used hereindescribes the defectivity performance obtained through the inclusion ofa compound having formula (I) in the chemical mechanical polishingcomposition used for the chemical mechanical polishing method of thepresent invention means that at least the following expression issatisfied:X<X₀wherein X is the defectivity (i.e., post CMP/hydrogen fluoride (HF)scratches or defects) for a chemical mechanical polishing compositioncontaining the substances used in the method of the present invention,as measured under the polishing conditions set forth in the Examples;and X₀ is the defectivity (i.e., post CMP/hydrogen fluoride scratches ordefects) obtained under identical conditions with only silica abrasivespresent.

Preferably, the chemical mechanical polishing compositions of thepresent invention include a quaternary phosphonium compound in amountsof 0.001 to 1 wt %, more preferably, from 0.01 to 1 wt %, mostpreferably, from 0.1 to 0.5 wt %.

Exemplary quaternary phosphonium compounds are tetraphenyl phosphoniumbromide, tetraphenyl phosphonium chloride, benzyltriphenyl phosphoniumbromide, benzyltriphenyl phosphonium chloride, ethyltriphenylphosphonium bromide, ethyltriphenyl phosphonium chloride,methyltriphenyl phosphonium bromide and methyltriphenyl phosphoniumchloride. Mixtures of such quaternary phosphonium compounds can beincluded in the chemical mechanical polishing compositions of thepresent invention.

The water contained in the chemical mechanical polishing compositionused in the chemical mechanical polishing method of the presentinvention is preferably at least one of deionized and distilled to limitincidental impurities.

The chemical mechanical polishing composition used in the chemicalmechanical polishing method of the present invention contains 0.1 to 40wt % abrasive; preferably, 5 to 30 wt % abrasive, more preferably, 10 to20 wt %. The abrasive used preferably has an average particle size of<200 nm; more preferably 75 to 150 nm; most preferably 100 to 150 nm.

Abrasives for use in the chemical mechanical polishing composition usedin the chemical mechanical polishing method of the present inventioninclude, for example, inorganic oxides, inorganic hydroxides, inorganichydroxide oxides, metal borides, metal carbides, metal nitrides, polymerparticles and mixtures comprising at least one of the foregoing.Suitable inorganic oxides include, for example, silica (SiO₂), alumina(Al₂O₃), zirconia (ZrO₂), ceria (CeO₂), manganese oxide (MnO₂), titaniumoxide (TiO₂) or combinations thereof. Modified forms of these inorganicoxides, such as, organic polymer coated inorganic oxide particles andinorganic coated particles can also be utilized if desired. Suitablemetal carbides, borides and nitrides include, for example, siliconcarbide, silicon nitride, silicon carbonitride (SiCN), boron carbide,tungsten carbide, zirconium carbide, aluminum boride, tantalum carbide,titanium carbide, or combinations thereof.

The preferred abrasive for use in the chemical mechanical polishingcomposition used in the chemical mechanical polishing method of thepresent invention is colloidal silica. Preferably, the colloidal silicaused contains at least one of precipitated silica and agglomeratedsilica. Preferably, the colloidal silica used has an average particlesize of <200 nm, more preferably, 75 to 150 nm, most preferably, 100 to150 nm; and accounts for 0.1 to 40 wt %, preferably, 5 to 30 wt %, morepreferably, 10 to 20 wt % of the chemical mechanical polishingcomposition. Examples of commercially available colloidal silica areKlebosol™ II 1630 colloidal silica with 139 nm average particle size;Klebosol™ II 1630 colloidal silica with 145 nm average particles size;and Klebosol™ II 1730 colloidal silica with 130 nm particle size allmanufactured by Merck KgAA, Darmstadt, Germany, all available fromDuPont.

Optionally, the chemical mechanical polishing composition containsbiocides, such as KORDEK™ MLX (9.5-9.9% methyl-4-isothiazolin-3-one,89.1-89.5% water and <1.0% related reaction product) or KATHON™ ICP IIIcontaining active ingredients of 2-methyl-4-isothiazolin-3-one and5-chloro-2-methyl-4-isothiazolin-3-one, each manufactured byInternational Flavors & Fragrances, Inc., (KATHON and KORDEK aretrademarks of International Flavors & Fragrances, Inc.).

When biocides are included in the chemical mechanical polishingcomposition of the present invention, the biocides are included inamounts of 0.001 wt % to 0.1 wt %, preferably, 0.001 wt % to 0.05 wt %,more preferably, 0.001 wt % to 0.01 wt %, still more preferably, 0.001wt % to 0.005 wt %.

The chemical mechanical polishing composition used in the chemicalmechanical polishing method of the present invention has a pH of >7,preferably 7 to 12, more preferably 10 to 11.

The chemical mechanical polishing composition used can optionallyinclude one or more pH adjusting agent to maintain the pH within apreferred range. Preferably, the pH adjusting agent is chosen from oneor more of sodium hydroxide, potassium hydroxide, and ammonium salts,such as halide or nitrate salts.

The substrate polished in the chemical mechanical polishing method ofthe present invention comprises silicon oxide. The silicon oxide in thesubstrate includes, but is not limited to, borophosphosilicate glass(BPSG), plasma enhanced tetraethyl ortho silicate (PETEOS), thermaloxide, undoped silicate glass, high density plasma (HDP) oxide.

The chemical mechanical polishing pad used in the chemical mechanicalpolishing method of the present invention can by any suitable polishingpad known in the art. The chemical mechanical polishing pad can,optionally, be chosen from woven and non-woven polishing pads. Thechemical mechanical polishing pad can be made of any suitable polymer ofvarying density, hardness, thickness, compressibility and modulus. Thechemical mechanical polishing pad can be grooved and perforated asdesired.

The quaternary phosphonium compound having formula (I) contained in thechemical mechanical polishing composition used in the chemicalmechanical polishing method of the present invention results in animproved polishing defectivity performance. Preferably, the inclusion ofthe quaternary phosphonium compounds having formulae (I) in the chemicalmechanical polishing compositions provides a >50% reduction in polishingdefectivity (i.e., post CMP/hydrogen fluoride scratches), as measuredunder the polishing conditions set forth in the Examples. That is, atleast the following equations is preferably satisfied:(X ₀ −X)/X ₀*100>50;wherein X is the polishing defectivity (i.e., post CMP/hydrogen fluoridescratches or defects) for a chemical mechanical polishing compositioncontaining the quaternary phosphonium compound according to formula (I)and used in the method of the present invention, as measured under thepolishing conditions set forth in the Examples; and X₀ is the polishingdefectivity (i.e., post CMP/hydrogen fluoride scratches or defects)obtained under identical conditions with only silica abrasives present,or silica abrasive and a symmetrical quaternary phosphonium compound.

The chemical mechanical polishing composition used in the chemicalmechanical polishing method of the present invention enables operationwith a low nominal polishing pad pressure, for example at 3 to 35 kPa.The low nominal polishing pad pressure improves polishing performance byreducing scratching and other undesired polish defects and minimizesdamage to fragile materials.

The following examples are intended to illustrate the present inventionbut are not intended to limit its scope.

In the following Examples, unless otherwise indicated, conditions oftemperature and pressure are ambient temperature and standard pressure.

The following materials were used in the Examples that follow:

The polishing removal rate experiments were performed on eight-inchblanket wafers. An Applied Materials Mirra® polisher was used forexamples 1-2 and an Applied Materials Reflexion® polisher was used forexamples 3-4. Polishing examples 1-2 were performed using an VisionPad5000/K7™ polyurethane polishing pad and polishing examples 3-4 wereperformed using an IC1010 polyurethane polishing pad (both commerciallyavailable from Rohm and Haas Electronic Materials CMP Inc.) with a downforce of 20.7 kPa (3 psi), a chemical mechanical polishing slurrycomposition flow rate of 150 mL/min in examples 1-2 and 250 mL/min inexamples 3-4, a table rotation speed of 93 rpm and a carrier rotationspeed of 87 rpm. The removal rates were determined by measuring the filmthickness before and after polishing using a KLA-Tencor FX200 metrologytool. The defectivity performances reported in the Examples wasdetermined using a Scanning Electron Microscope after a hydrogenfluoride post polishing wash (“Pst HF”). All the TEOS wafers afterPst-HF wash were inspected using a Surfscan® SP2 defect inspectionsystem available from KLA-Tencor. The defects information, includingtheir coordinates on the wafer, was recorded in KLARF (KLA Results File)which was then transferred to eDR-5200 defect review system availablefrom KLA-Tencor. A random sample of 100 defect images were selected andreviewed by eDR-5200 system. These 100 images were classified intovarious defect types, for example, chatter marks (scratches), particlesand pad debris. Based on classification results from these 100 images,the total number of scratches on the wafer was determined.

EXAMPLE 1 Chemical Mechanical Polishing Compositions, TEOS RR and DefectReduction

Aqueous chemical mechanical polishing slurries were prepared as shown inTable 1 below. Aqueous 2 wt % KOH as added to each slurry to maintainthe desired pH.

TABLE 1 Benzyltriphenyl Methyltriphenyl Phosphonium Phosphonium AbrasiveChloride Bromide Slurry (wt %) (wt %) (wt %) pH PC-1 16 0 0 10.7 SC-1 160.081 0 10.7 SC-2 16 0 0.074 10.7Abrasive: Klebosol™ II 1630 colloidal silica with 139 nm averageparticle size manufactured by Merck KgAA, Darmstadt, Germany, availablefrom DuPont.

TABLE 2 TEOS Pst-HF Pst-HF Slurry RR Defect Counts Scratches PC-1 3881515 486 SC-1 4041 246 119 SC-2 4089 188 100The slurries of the invention showed significant TEOS RR and reduceddefect counts and reduced scratches in comparison to the comparativeslurry.

EXAMPLE 2 Chemical Mechanical Polishing Compositions, TEOS RR and DefectReduction

Aqueous chemical mechanical polishing slurries were prepared as shown inTable 3 below. Aqueous 2 wt % KOH as added to each slurry to maintainthe desired pH.

TABLE 3 Tetrabutyl Tetraphenyl Phosphonium Phosphonium Abrasive BromideChloride Slurry (wt %) (wt %) (wt %) pH PC-2 16 0 0 10.7 PC-3 16 0.09 010.7 SC-3 16 0 0.1 10.7Abrasive: Klebosol™ II 1630 colloidal silica with 139 nm averageparticle size manufactured by Merck KgAA, Darmstadt, Germany, availablefrom DuPont.

TABLE 4 TEOS Pst-HF Pst-HF Slurry RR Defect Counts Scratches PC-2 2868638 422 PC-3 2811 600 204 SC-3 3165 232 151The slurry of the invention which included tetraphenyl phosphoniumchloride exhibited enhanced TEOS RR and reduced defects and scratchescompared to the two comparatives.

EXAMPLE 3 Chemical Mechanical Polishing Compositions, TEOS RR andScratch Reduction

Aqueous chemical mechanical polishing slurries were prepared as shown inTable 3 below. Aqueous 2 wt % KOH as added to each slurry to maintainthe desired pH.

TABLE 5 Methyltriphenyl Tetraphenyl Phosphonium Phosphonium AbrasiveBromide Chloride Slurry (wt %) (wt %) (wt %) pH PC-4 15.5 0 0 10.7 SC-415.5 0.074 0 10.7 SC-5 15.5 0.05 0 10.7 SC-6 15.5 0.1 0 10.7 SC-7 15.5 00.078 10.7 SC-8 15.5 0 0.052 10.7 SC-9 15.5 0 0.104 10.7Abrasive: Klebosol™ II 1630 colloidal silica with 139 nm averageparticle size manufactured by Merck KgAA, Darmstadt, Germany, availablefrom DuPont.

TABLE 6 Pst-HF Slurry TEOS RR Scratches PC-4 2899 311 SC-4 3101 120 SC-53049 179 SC-6 3044 65 SC-7 3113 176 SC-8 3080 124 SC-9 3171 175The slurries of the invention had significantly increased TEOS RR andreduced scratches in comparison to the comparative slurry which excludedthe quaternary phosphonium compounds.

EXAMPLE 4 Stability of Chemical Mechanical Polishing Compositions

Aqueous chemical mechanical polishing compositions were prepared to testtheir stability. The pH of the compositions was maintained at 10.7. Thesample were left at static conditions of room temperature and pressurefor 2 weeks then visually checked.

TABLE 7 Methyltriphenyl Tetraphenyl Phosphonium Phosphonium AbrasiveBromide Chloride Colloidal Pst-HF Slurry (wt %) (mmol) (mmol) StabilityScratches PC-5 15.5 0 0 Stable 311 SC-10 15.5 0.0021 0 Stable 120 SC-1115.5 0.0014 0 Stable 179 SC-12 15.5 0.0028 0 Stable 65 SC-13 15.5 0.00500 Very — thick SC-14 15.5 0.0080 0 Com- — pletely gelled SC-15 15.5 00.0021 Stable 176 SC-16 15.5 0 0.0014 Stable 124 SC-17 15.5 0 0.0028Stable 175 SC-18 15.5 0 0.0050 Very — thick SC-19 15.5 0 0.0080 Com- —pletely gelledAbrasive: Klebosol™ II 1630 colloidal silica with 139 nm averageparticle size manufactured by Merck KgAA, Darmstadt, Germany, availablefrom DuPont.

The chemical mechanical polishing compositions of the present inventionwere stable where the quaternary phosphonium compounds were atconcentrations of 0.0021-00028 mmols.

What is claimed is:
 1. A chemical mechanical polishing compositionconsisting of water; an abrasive; optionally a pH adjusting agent;optionally a biocide; a pH greater than 7; and a quaternary phosphoniumcompound having formula (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, I⁻, F⁻ and OH⁻.
 2. The chemical mechanicalpolishing composition of claim 1, wherein the chemical mechanicalpolishing composition consists of the water; 0.1 to 40 wt % of theabrasive; optionally the pH adjusting agent; optionally the biocide; thepH greater than 7; 0.001 to 1 wt % of the quaternary phosphoniumcompound having the formula (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, I⁻, F⁻ and OH⁻.
 3. The chemical mechanicalpolishing composition of claim 1, wherein the chemical mechanicalpolishing composition consists of the water; 5 to 25 wt % of theabrasive, wherein the abrasive is a colloidal silica abrasive; the pHadjusting agent; the biocide; a pH of 8-13; 0.01 to 1 wt % of thequaternary phosphonium compound having the formula (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, Cl⁻, I⁻, F⁻ and OH⁻.
 4. The chemical mechanicalpolishing composition of claim 3, wherein the pH adjusting agent isselected from the group consisting of potassium hydroxide, sodiumhydroxide, ammonium salts and mixtures thereof.
 5. The chemicalmechanical polishing composition of claim 1, wherein the quaternaryphosphonium compound is selected from the group consisting oftetraphenyl phosphonium bromide, tetraphenyl phosphonium chloride,benzyltriphenyl phosphonium bromide, benzyltriphenyl phosphoniumchloride, ethyltriphenyl phosphonium bromide, ethyltriphenyl phosphoniumchloride, methyltriphenyl phosphonium bromide, methyltriphenylphosphonium chloride and mixtures thereof.
 6. A method for chemicalmechanical polishing of a substrate, comprising: providing a substrate,wherein the substrate comprises silicon oxide; providing a chemicalmechanical polishing composition consisting of water; an abrasive;optionally a pH adjusting agent; optionally a biocide; a pH greater than7; a quaternary phosphonium compound having (I):

wherein R is selected from the group consisting of phenyl, benzyl, andlinear or branched C₁-C₄ alkyl; and X is an anion selected from thegroup consisting of Br⁻, Cl⁻, I⁻, F⁻ and OH⁻; providing a chemicalmechanical polishing pad with a polishing surface; creating dynamiccontact at an interface between the polishing surface of the chemicalmechanical polishing pad and the substrate with a down force of 3 to 35kPa; and dispensing the chemical mechanical polishing composition ontothe chemical mechanical polishing pad at or near the interface betweenthe chemical mechanical polishing pad and the substrate; and whereinsome of the silicon oxide is removed from the substrate.
 7. The methodof chemical mechanical polishing a substrate of claim 6, wherein thequaternary phosphonium compound is selected from the group consisting oftetraphenyl phosphonium bromide, tetraphenyl phosphonium chloride,benzyltriphenyl phosphonium bromide, benzyltriphenyl phosphoniumchloride, ethyltriphenyl phosphonium bromide, ethyltriphenyl phosphoniumchloride, methyltriphenyl phosphonium bromide, methyltriphenylphosphonium chloride and mixtures thereof.